1. Field of the Invention
The present invention relates to an IP telephone apparatus, an ENUM server, and a calling method via the Internet.
2. Description of Related Art
The recent rapid growth of the Internet has drawn attention to an IP telephone system that enables low-cost voice communications with telephone apparatuses at remote places as well as free voice communications between IP telephone apparatuses owned by subscribers. It is also known that, when a PSTN (Public Switched Telephone Network) (hereafter referred to as PSTN) telephone apparatus connected to a conventional PSTN places a call to an IP telephone apparatus, a telephone number which begins with “050” is dialed. Some IP telephone apparatuses are able to have a conventional PSTN telephone function as well and can use a telephone number in an OABJ system as well as an IP telephone number.
The telephone apparatus described in Related Art 1 also functions as an IP telephone apparatus. When the telephone apparatus functions as a conventional PSTN telephone as well as an IP telephone apparatus, the telephone apparatus maintains a PSTN telephone number as well as an IP address. When receiving or placing a call, the telephone apparatus transmits, to another telephone apparatus, an IP address of the telephone apparatus. The telephone apparatus then determines whether another telephone apparatus is an IP telephone apparatus or a PSTN telephone apparatus by checking whether there is a response to the transmitted IP address from another telephone apparatus. The telephone apparatus then makes interconnection with another telephone apparatus as a source IP telephone apparatus or a destination IP telephone apparatus (or PSTN telephone apparatus), via either the IP network or the PSTN.    [Related Art 1] Japanese Laid Open Publication 2003-125032
However, when placing a call to the IP telephone apparatus that has the PSTN telephone function as well and that can use both PSTN telephone numbers in the OABJ system and IP telephone numbers, users on the transmitting side need to memorize PSTN telephone numbers as well as IP telephone numbers, which has been a burden to those users.
Also, the telephone apparatus described in Related Art 1 that functions as an IP telephone apparatus, when placing a call to another IP telephone apparatus (or PSTN telephone apparatus), transmits, to another telephone apparatus, the IP address of the telephone apparatus, at the reception or transmission of a call. The telephone apparatus then determines whether another telephone apparatus is an IP telephone apparatus or a PSTN telephone apparatus by checking whether there is a response to the transmitted IP address from another telephone apparatus. The IP telephone apparatus then makes interconnection with another telephone apparatus via either the IP network or the PSTN. This system does not reduce the workload for users of the IP telephone apparatus, because they need to memorize both PSTN telephone numbers and IP telephone numbers.